Changing the C354 for the 50 ohm resistor will give better filtering. Dynaco probably didn't use it to save money. You don't really have to change the other power supply components. I don't know what the stock voltage rating of the second 40mf cap is but I would use 500v rated caps to be safe. The choke will probably cause a few initial spikes due to the inrush current. (not a problem with tube rectifiers)
With modern diodes and capacitors, I might consider eliminating the 95 ohm resistor across the first 100 ohm cap and add an inrush limiter in the power trannt primary.
The Dynaclones should work fine with no circuit changes needed.
Stereo 35i?!
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by mesherm » Tue Mar 07, 2006 3:37 pm
I apologize for my bad eyes and old ST35 schematic. I was looking at the 100uf/95 ohm combo and assuming it was in the power supply but it is the cathode resistor/cap....bad bifocals..
The power supply is just a 50 ohm resistor into a 40uf cap (an RC filter) which feeds the output tubes then a 6.8k resistor and a 20uf cap ( another RC filter) for the amp/phase inverter power.
If you simply replace the 50 ohm with the C354 it will drop your B+ voltage a lot. If you want to replace the 50 ohm with a C354 then wire another 20 to 40uf cap BEFORE the choke also. That will give much better filtering. It will probably raise your B+ about 10 volts.
Chokes (inductors) impede the flow of alternating current. The more the current tries to alternate the more the inductor resists (like nagging your grandson to cut your lawn). By putting the choke first, all the rectified DC is tryng to flow through the choke thus raising its effective impedance and making it appear to be a much larger resistance. By insering a capacitor before the choke, the choke smooths out the fluctuating DC some and lowers the effective impedance of the choke now that the current "humps" are reduced.
The power supply is just a 50 ohm resistor into a 40uf cap (an RC filter) which feeds the output tubes then a 6.8k resistor and a 20uf cap ( another RC filter) for the amp/phase inverter power.
If you simply replace the 50 ohm with the C354 it will drop your B+ voltage a lot. If you want to replace the 50 ohm with a C354 then wire another 20 to 40uf cap BEFORE the choke also. That will give much better filtering. It will probably raise your B+ about 10 volts.
Chokes (inductors) impede the flow of alternating current. The more the current tries to alternate the more the inductor resists (like nagging your grandson to cut your lawn). By putting the choke first, all the rectified DC is tryng to flow through the choke thus raising its effective impedance and making it appear to be a much larger resistance. By insering a capacitor before the choke, the choke smooths out the fluctuating DC some and lowers the effective impedance of the choke now that the current "humps" are reduced.
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mesherm - KT88
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by mesherm » Tue Mar 07, 2006 5:15 pm
Corgrats for even geting your hands on a ST35. The prices for an ST35 on ebay are off-world. Even a old bare chassis and cage went for like $150. I will have to keep my eyes open for one of soundtastiks ST35 chassis. I have the trannies from an old SCA-35 and Roy has the PCBs.
Just what I need, more amplifiers....but I can't stop....arrrgggg Yellow_Light_Colorz_PDT_09
Just what I need, more amplifiers....but I can't stop....arrrgggg Yellow_Light_Colorz_PDT_09
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mesherm - KT88
- Posts: 1232
- Joined: Fri Aug 27, 2004 10:33 pm
- Location: Alvin Texas
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